"If LeBron wanted to fight with me, it wouldn't be close!"

That's UFC fighter Bobby Green aka "King" saying he'd wash Bron in a purely hypothetical fight for the royal nickname.

See, TMZ Sports was talking to the 37-year-old lightweight before his Fight Night main event scrap against 29-year-old Grant Dawson, the 10th ranked 155 pounder.

Dawson's nickname is "KGD" ... said to stand for "King Grant Dawson"

When we asked Green if he had a message for Grant, he told us ... "There can only be one King. I just found out that Grant Dawson's fight name is KGD. There can only be one king. Let's go find out. The other one's gonna get his head cut off!"

Okay, okay. Obviously, the most famous "King" going right now this side of Charles is LeBron ... and given the age-old debate about skill vs. size, we asked BG if he could beat the 6'8" hoops legend.

"It wouldn't be close!" Bobby said.

We mentioned the size discrepancy ... Bobby's 5'10" and fights at 155 lbs. (we'll assume he walks around in the neighborhood of 185). James is 10 inches taller, and weighs 250 lbs., according to the Lakers website.

Irrelevant, according to Bobby.

"He's a big dude but he doesn't have the skills I'm sorry. Skills pay the bills, sir."

But, would Green actually fight King James?

"In a drop of a dime. In a heartbeat, without even thinking about it. Hell yeah. I'll wax his ass!"